Magnetic resonance imaging (NMRI) is a diagnostic technique which produces high resolution images of internal organs without using ionizing radiation. In forming these images, the nuclei of hydrogen atoms (the most abundant element in the body, largely in the form of H.sub.2 O) are first aligned with a large magnetic field, then excited with a radiofrequency (Rf) pulse to induce flipping of the nuclei and orientation against the field, and finally, detection of the emitted Rf signal during the reorientation process which occurs after the cessation of the Rf pulse. The strength and rate of change in the strength of the emitted signals depend upon the number of nuclei involved and the characteristic relaxation times (spin-lattice relaxation times or T.sub.1 and spin-spin relaxation times or T.sub.2) associated with the chemical surroundings of the nuclei. By applying small magnetic field gradients to a volume of material and changing the direction of these gradients, spatial information can be decoded from the signal. Mathematical manipulation then allows construction of an image on a cathode ray tube in a manner similar to data from X-ray computed tomography (CT). The radiofrequency radiation employed is well below that of X-rays, is non-ionizing, and is considered to be incapable of causing any damage to molecules of living cells. There is a small amount of tissue heating which is believed to be clinically insignificant.
Cervical malformations, malpositions and tumors do not often interfere with conception, but they may be a factor in faulty nidation and early abortion. Submucous myomas may obstruct the uterine ends of the tube and thus prevent fertilization or may distort the uterine cavity and interfere with nidation. Partial or complete occlusion of the fallopian tubes is an important etiological factor in infertility, encountered in about 30% of all women who fail to conceive. Tubal obstruction usually results from the destructive effect of pathogenic microorganisms on the mucosal surface. Gonorrheal salpingitis is an important cause of obstruction or restriction, but not the only one. Bacteria regularly ascend from the infected uterine cavities of women who have aborted or have had a normal delivery, and may produce a destructive endosalpingitis. Uterine fibroids or cornual adenomyosis may distort and occlude the uterine ends of the tubes. The tubes can also be kinked or occluded by adhesions after appendicitis or other infections or areas of pelvic endometriosis. Sometimes, intermittent obstruction occurs because of spasm of the uterine ends of the tubes.
Procedures for examining for fallopian tubal patency include uterotubal insufflation (Rubin's test), injecting a gas such as carbon dioxide into the uterine cavity under pressure and recording the alterations in pressure can detect total blockage of the tubes. Hysterosalipingography (HS) employs X-ray visualization of the uterine cavity and the tubal lumina after the injection of an opaque dye into the upper genital tract. Pneumohysterosalpingography (PHS) is similar to HS but uses X-ray imaging during sequential insufflation with gas and with an opaque dye. Laparoscopy involves direct observation of the passage of dye from the ends of the fallopian tubes through optical devices inserted through small incisions in the abdominal area. Culdoscopy is similar to laparoscopy, but the optical device is inserted through an incision in the vaginal vault.
Rubin's test has fallen into disuse, and techniques providing more information have been developed. The best current method involves the invasive techniques of laparoscopy and culdoscopy using a dye such as methylene blue. These require anesthesia and surgical procedures, with attendant risks.
Hysterosalpingography and PHS avoid the use of anesthia and surgery. They require the injection of a radiopaque dye through the cervix uteri and monitoring by fluoroscope and film to provide a permanent record of the shape of the uterine cavity and fallopian tubes. However, despite development of faster procedures and use of lower levels of X-rays, the radiation dosage to which the ovaries are exposed during this procedure are believed to provide a serious risk of genetic damage and birth defects. Muller, H. in Am. J. Obstet. Gynecol. 67: 463 (1954) has stated in regard to irradiation of the gonads that there is "no dose so small as to give no mutations at all; each individual ionization and probably each activation of an atom carries its definite chance of producing a mutation." Sheikh, H. et al in Am. J. Obstet. Gynecol, 124(3): 307-310 states that, "On the average, each newly mutated gene, no matter how small the detriment it occasions, eventually takes its toll in the form of making a major contribution to the extinction of the line of descent." Furthermore, these procedures are not easily susceptible to tomographic analysis.
Ultrasound and CT have been applied to examine the pelvic area including the cervix and ovaries. The lack of definition in ultrasound methods renders them useless in determining the presence of obstructions or other endothelial deformations of the fallopian tubes. CT methods are limited by the inability to distinguish between soft materials having closely similar X-ray absorption characteristics. They are also subject to distortion due to metal clips, contrast media and bone density. As a result, neither of these procedures are used in determination of fallopian tubal patency.
More recently, NMRI techniques are being developed for imaging the pelvic regions. Hamlin, D. et al, AJR. 145: 585-590 (1985) reports the study of ovarian masses in patients using NMRI. McCarthy, S. in Magnetic Resonance Imaging, 4:59-66 (1986) indicates the uterine fundus, isthmus, cervix and vagina are easily identified in NMRI. The ovaries appear as medium intensity structures, with increase in intensity with T.sub.2, blending with fat. Follicles can be accentuated on long TR, TE sequences. Hricak, H. in AJR. 146: 1115-1122 (1986) using the 0.35 T MT/S system of DIASONICS (Milpitas, CA) reported that normal ovaries were most difficult to demonstrate on NMRI. While more recent improved machines have reduced these difficulties, most advance imaging equipment and methods do not provide an image of fallopian tubes with sufficient contrast and detail to determine patency. Ovaries and fallopian tubes have a low to medium signal intensity on the T.sub.1 -weighted image (short TR and TE). When TR is short, distinguished ovaries from the surrounding bowel is difficult. When TR is longer, ovarian signal intensity increases and approaches that of the surrounding fat.
Prior to this invention, the image definition available with most advanced NMRI procedures and equipment was unable to provide the definition required to evaluate fallopian tubal patency.